Precise information of relative attitude between remote objects is necessary for a variety of reasons. For instance, in a spacecraft it is often important to determine variances in attitude between the inertial reference platform and objects such as boom mounted, steerable antennas, remote sensor platforms and STS pallet-mounted experiments to name a few. Such attitude information is necessary so that data received from or provided to such objects may be corrected or calibrated for relative deviation in attitudes between the inertial reference platform and the object of interest.
Use of star trackers or gyros to obtain attitude information for individual objects is often prohibitive in cost as well as space and weight requirements. Thus, systems which measure attitude without the necessity that each object include its own attitude sensing apparatus are highly desirable and, in fact, are in existence today.
One such system requires two transmitter/receiver assemblies mounted, e.g., on the inertial reference platform. One transmitter/receiver measures pitch and yaw through autocollimation by reflecting a beam of monochromatic light from a mirror mounted on the remote platform whose attitude is to be measured. Sensors in the transmitter/receiver provide information of the pitch and yaw. The second transmitter/receiver is necessary to determine roll of the remote platform.
A second system ultilizes a single transmitter/receiver. Pitch and yaw are obtained as above but roll is obtained through the use of an active source which must be mounted on the remote platform to direct a beam of polarized light back to the transmitter/receiver.
The present invention is an improvement over the above described systems and requires only a single transmitter/receiver on the inertial reference platform without the necessity of active sources mounted on the remote platform.